1. Field of the Invention
The present invention relates to the attainment of efficient shifting of laser radiation using stimulated Raman scattering in atomic vapor and molecular media, the control of the generated beam quality spectral bandwidth as well as scaling to larger energies and power levels being accomplished using coupled, unstable resonators consisting of partially transmissive optics. This results in a sequence of laser and Stokes radiation amplification which results in high conversion efficiency and a beam output with low divergence.
2. Description of the Prior Art
Attainment of efficient wavelength shifting of laser radiation has been widely demonstrated using stimulated Raman scattering in atomic vapor and molecular media. However, control of the generated beam quality and spectral bandwidth as well as scaling to the larger energy and power levels have required the use of sophisticated optical configurations such as master-oscillator/power amplifiers and unstable resonators. Prior art disclosures relating to master-oscillator/power amplifiers are disclosed for example in the article by Komine et al "Efficient Higher-Stokes-Order Raman Conversion in Molecular Gases", Opt. Lett. 4, 398 (1979); Komine et al, Higher-Stokes-Order Raman Conversion of XeCl Laser in Hydrogen, Opt. Lett. 7, 157 (1981); Komine et al, "Efficient H Raman Conversion of Long-Pulse XeF Laser Radiation into Blue-Green Region", Appl. Phys. Lett. 4, 551 (1980) and U.S. Pat. No. 4,280,109. Typical of the prior art describing unstable resonators providing the above features is described in the article by Woods et al, "Aperture Combined Raman Laser", AIP Conference Proceedings No. 100, Series on Optical Science and Engineering No. 3, Excimer Laser-1983, p. 200 (1983).
In a number of applications requiring a specific laser frequency, it is required that the output beam from the Raman converter have a uniform intensity profile and low divergence using a minimum number of optical components. Raman converter optical configurations using a master-oscillator/power amplifier technique satisfy the beam profile and divergence requirements, but generally require many optical elements to achieve the necessary beam sizes and intensity levels for optimum performance. Unstable resonators formed by a pair of reflective mirrors for the Stokes radiation provide a more simplified optical cavity design; however, an off-axis pumping geometry is normally needed to couple the laser radiation into the Raman resonator cavity. The disadvantages to this approach is that such off-axis pumping geometry imposes a very stringent narrow spectral bandwidth requirement on the laser radiation which may be difficult to achieve in particular lasers.
Furthermore, the output provided by the unstable resonators is partially obscured resulting in an irregular shaped beam or a beam with a hole inside.
What is desired therefore is to provide a device for shifting the wavelength of laser radiation using stimulated Raman scattering in atomic vapor and molecular media wherein the beam intensity profile is substantially uniform, and the beam divergence is low, the device providing relatively high conversion efficiency in addition to using a minimum number of optical elements to achieve the necessary beam sizes and intensity levels for optimum performance.